Note the LIST is prepended whole, not one element at a time, so the
prepended elements stay in the same order. Use reverse to do the
reverse.

Starting with Perl 5.14, unshift can take a scalar EXPR, which must hold
a reference to an unblessed array. The argument will be dereferenced
automatically. This aspect of unshift is considered highly
experimental. The exact behaviour may change in a future version of Perl.

To avoid confusing would-be users of your code who are running earlier
versions of Perl with mysterious syntax errors, put this sort of thing at
the top of your file to signal that your code will work only on Perls of
a recent vintage: